Field of the Invention
The present invention relates to cosmetic or dermatological formulations, in particular UV radiation protection formulations.
The skin is an important, but at the same time sensitive, human organ, the care of which is essential for physical and psychological well-being. A large number of skin care compositions have been developed, which are supplied as creams, lotions, oils or gels and contain special skin care active ingredients.
Cosmetic and dermatological skin care compositions are primarily used in order to intensify or restore the natural function of skin as a barrier against environmental influences (for example dirt, chemicals, microorganisms) and against the loss of endogenous substances (for example water, natural fats, electrolytes).
If this function is impaired, increased absorption of toxic or allergenic substances or attack by microorganisms and, as a consequence, toxic or allergic skin reactions may occur.
The aim of cosmetic skin care is furthermore to compensate the loss of fats and water from the skin caused by daily washing. This is important especially if the natural regeneration capacity is inadequate. Skin care products furthermore should protect against environmental influences, in particular sun and wind, and delay the signs of ageing of the skin.
The damaging effect of the ultraviolet part of solar radiation on the skin is generally known. While rays having a wavelength in the range from 200-280 nm (the so-called UVC range) are completely absorbed by the ozone layer in the earth's atmosphere, rays in the range between 280 nm and 315 nm, the so-called UVB range, cause erythema, simple sunburn or even burns of greater or lesser severity on the skin.
Numerous water-soluble or lipid-soluble organic UV filter substances (chemical sunsreen filter substances) are known for protection against UVB radiation, most of these substances being derivatives of 3-benzylidenecamphor, of 4-aminobenzoic acid, of cinnamic acid, of salicylic acid, of benzophenone and also of 2-phenylbenzimidazole (e.g. 2-phenylbenzimidazole-5-sulfonic acid sodium salt). Other examples of UV filter substances can be found in the literature.
UV filter substances are also important for the wavelength range between about 315 and 400 nm, the so-called UVA range, since such rays can also cause damage. It has thus been proved that UVA radiation leads to damage to the elastic and collagenic fibers of the connective tissue, which makes the skin age prematurely and is to be regarded as a cause of numerous phototoxic and photoallergic reactions. The damaging influence of UVB radiation may be intensified by UVA radiation.
UV radiation can also lead to photochemical reactions, the photochemical reaction products then intervening in skin and cell metabolism.
Such photochemical reaction products are chiefly free radical compounds, for example hydroxyl radicals, hydroperoxy radicals and superoxide ions. Further damage is caused by free radical photo-products which are formed in the skin itself and bear high reactivity. However, even singlet oxygen, an excited state of the oxygen molecule which is not in free radical form, can occur with UV irradiation, as can short-lived epoxides and many others. Singlet oxygen, for example, is distinguished from the triplet oxygen usually present (free radical base state) by an increased reactivity. Nevertheless, excited, reactive (free radical) triplet states of the oxygen molecule also exist.
To prevent these reactions, antioxidants and/or agents which trap the radicals can be incorporated into the cosmetic or dermatological formulations, typically in addition to organic UV filter substances.
Furthermore, coated or uncoated inorganic pigments which are known to be used in sunscreen products can help to protect the skin from UV rays. Most inorganic pigments used in cosmetics to protect the skin from UV rays are UV absorbers or UV reflectors. These are oxides of titanium, zinc, iron, zirconium, silicon, manganese, aluminium, cerium and mixtures thereof, as well as modifications. Inorganic pigments are typically used in addition to organic UV filter substances.
Numerous sunscreen compositions (sun protection products) are known for protection against the detrimental effects of exposure to sunlight (UVA and UVB). For various reasons associated especially with being more pleasant to use (gentleness, emollience, ease of application and the like) the sunscreen compositions currently available are typically (but not always) oil-in-water emulsions (namely, a cosmetically acceptable vehicle, carrier or diluent) comprising an aqueous continuous dispersion phase and an oily discontinuous dispersed phase which contain, at various concentrations, one or more organic UV filter substances which are capable of selectively absorbing harmful UV radiation, these filter substances being selected as a function of the degree of desired protection. However, one of the problems presented by this type of sunscreen composition is, in particular, the fact that, once they have been applied to the skin in the form of a film by the users thereof, they have relatively little resistance to water.
Light protection formulations are required and used particularly frequently on bathing beaches and in open-air swimming pools. It is in this case desirable for the light protection formulation to be largely water-resistant, that is to say for it to be washed off from the skin to only a small extent, if at all.
Higher light protection factors, that is to say, for example, those situated above SPF 15, can in general be achieved only by larger amounts of UV filter substances. If a sunscreen product is also still to have a high light protection factor after bathing, the UV filter substance in particular must be retained on the skin.
It is in itself already troublesome if the sunscreen product has to be applied again after bathing. During bathing itself, under certain circumstances the use of a light protection formulation which can be washed off is even irresponsible and harmful to the skin, since water absorbs light in the UVA and UVB range poorly, and consequently represents no noticeable UV protection, not even for submerged areas of skin.
Accordingly, a major object of the present invention is the provision of novel cosmetic or dermatological compositions, in particular sunscreen compositions, which have increased water resistance.
By the term "water resistance" is intended the stability, activity or effect over time of the active ingredient(s) of a given cosmetic or dermatological formulation.
With respect to sunscreen formulations the term "water resistance" is intended the stability over time of the degree of protection in the UVA and/or UVB ranges of sunscreen composition subjected (after application to the skin) to contact with water. The solar protection associated with a given composition is characterized by assigning it a sun protection factor (or SPF) which is mathematically expressed by the ratio of the exposure time necessary to attain the erythematous threshold (minimal erythemal dose) with the UV screen to the time necessary to attain the erythematous threshold without UV screen.
With respect to formulations comprising other (non-UV-protective) cosmetic and/or dermatological agent(s) the term "water resistance" refers to the activity or effect over time of the respective agent(s) of a formulation subjected (after application to the skin) to contact with water.
A further object of the invention is the provision of a method for imparting water resistance to or improving water resistance of a cosmetic or dermatological formulation comprising a cosmetic or dermatological agent in a cosmetically and/or pharmaceutically acceptable carrier (this term comprising all kinds of carriers, vehicles, diluents and the like) for application, in particular topical application, to the skin of humans or animals.